This invention relates in general to straightening of electronic component leads and, more specifically, to a method and apparatus for very precisely straightening and aligning high lead count, fine pitch, component leads on an electronic component.
Originally, printed circuit boards included plated holes into which leads of electronic components were inserted and soldered. Currently, circuit boards tend to have closely spaced surface pads with the component simply placed on the board with leads in contact with the pads, to which the leads are then soldered.
The pattern of closely spaced pads for connection to component leads are usually formed on the printed circuit board base by chemical etching techniques. After board fabrication and during assembly operations a stencil having through holes conforming to the pad pattern is placed over the pad array and precisely aligned therewith. A solder paste made up of very small solder balls in a slurry of flux and other ingredients is wiped over the stencil with a squeegee, forcing small amounts of paste through the holes onto the pads. The stencil is lifted away leaving the paste on the pads. The components must then be very precisely placed on the board with the component leads aligned with the pads. Typical so called "gull wing" type leads typically may have up to 376 leads with a lead-to-lead pitch of 0.4 mm. Once the component is placed, the solder is melted, generally in an infrared or convection oven, and bonds between the pad and lead.
With the very close spacing required over a very large number of leads, bent or twisted leads or leads that have ends out of the normal lead end plane cannot be mounted by this method. During production mounting, out of tolerance components are rejected. Many of the high rate component placement devices include vision equipment that senses out of tolerance conditions and reject those components. With inexpensive components, those rejected are usually scrapped. With the recent expensive very high density components repair of the leads is highly desirable.
Expensive, complex machines have been developed to bring component leads back into alignment. These machines are too expensive for small manufacturers. Further, they are not easily convertible to handle different components, so are not efficient for short run production.
Technicians will often try to use probes to attempt to bend leads back into alignment. This requires considerable skill and often results in lead damage or breakage. While one lead is being straightened, adjacent leads may be inadvertently contacted and damaged. In particular, it is difficult to align the ends of a large number of leads into a common plane and to correct twisted lead ends. Imperfect corrections will lead to problems when the component is mounted and soldered to a board.
Thus, there is a continuing need for methods and devices for realigning electronic component leads that is low in cost, does not require highly skilled technicians and can rapidly and effectively return the lead array to an "in tolerance" condition.